Method for manufacturing metal gasket for cylinder head, and metal gasket for cylinder head

ABSTRACT

Provided is a metal gasket for a cylinder head that is capable of improving engaging force between a substrate and a step adjustment plate. A method for manufacturing the metal gasket for a cylinder head includes the steps of: forming a prepared hole  3   c  in each of a plurality of protruding pieces  3   b  of the step adjustment plate  3;  forming a tubular portion  3   d  including a plurality of projecting segments  3   d   1  by inserting a die  4  including a polygonal pyramidal punch 4 a  into the prepared hole  3   c  so as to bend up a peripheral portion around the prepared hole  3   c  while cutting the peripheral portion into segments; forming in the substrate  2  an fastening hole  2   h  in correspondence with a position of the tubular portion  3   d  formed in the step adjustment plate  3;  and engaging the protruding piece  3   b  through the substrate  2  by inserting the tubular portion  3   d  of the step adjustment plate  3  through the corresponding fastening hole  2   h  formed in the substrate  2,  and subsequently folding the plurality of projecting segments  3   d   1  of the tubular portion  3   d  over to an outside of the substrate  2  and flattening out the projecting segments  3   d   1 .

TECHNICAL FIELD

The present invention relates to a method for manufacturing a metal gasket for a cylinder head that is interposed between a cylinder block and a cylinder head in an internal combustion engine to seal a joint surface between the cylinder block and the cylinder head, as well as such a metal gasket for a cylinder head.

BACKGROUND ART

In internal combustion engines, a metal gasket is interposed on a joint surface between a cylinder block and a cylinder head, and the metal gasket is fastened by head bolts for sealing of fuel gas, coolant, and lubricating oil. In particular, sealing of cylinder holes is crucial, because insufficient sealing of the cylinder holes can cause unwanted leakage flows of the fuel gas between adjacent cylinders, which might lead to a decrease in engine power. The leaked fuel gas can also flow into coolant holes circumferentially formed around the cylinder holes, resulting in malfunctions such as overheat, or in the worst case, engine seizure.

In an attempt to avoid the above phenomena, Patent Literatures 1, 2 disclose a metal gasket including a resilient metal layer in which annular beads are provided around the cylinder holes, for example. The metal gasket for a cylinder head disclosed in Patent Literatures 1 and 2 includes: a metal substrate made of a metal layer and having cylinder holes formed in correspondence with cylinder bores in a cylinder block of an internal combustion engine, annular beads formed around peripheries of the cylinder holes, coolant holes formed along peripheries of the annular beads in correspondence with a cooling water jacket of the cylinder block and coolant holes of the cylinder head; and an annular step adjustment plate provided to face the annular beads of the substrate. The step adjustment plate is provided with claw-shape portions, and these claw-shape portions are inserted into fastening holes formed in the substrate and folded over to one side so that the step adjustment plate is integrated with the substrate. Due to a thickness difference created by the step adjustment plate provided between the annular beads and outer beads, surface pressure is appropriately adjusted.

However, one problem with the technologies disclosed in Patent Literatures 1 and 2 is that, as shown in FIG. 18, the claw-shape portions 3 h are each folded over only to one side, and a step adjustment plate 3 cannot be strongly fastened with a substrate 2. Another problem is that, as shown in FIG. 19, when a plurality of step adjustment plates 3 are stacked on top of one another as inventory products or as components required in a manufacturing process of the metal gasket while the claw-shape portions 3 h are perpendicularly bent up from the step adjustment plate 3, some of the claw-shape portions 3 h are obliquely bent. Such an obliquely bent claw-shape portion 3 h can require increased man-hours due to a few alterations needed when the step adjustment plate 3 is assembled to the substrate 2, and the step adjustment plate 3 is sometimes scraped as a defective.

In view of the above problems, the present inventors conducted studies and they revealed that, as shown in FIGS. 20A and 20B, a strong coupling of the step adjustment plate 3 with the substrate is achieved by providing a prepared hole 3 c in a protruding piece 3 b projecting from a peripheral edge of the step adjustment plate 3, applying drawing to a peripheral portion around the prepared hole 3 c with use of a die including a cylindrical punch so as to form a tubular portion 3 d having a circular cross section, inserting the formed tubular portion 3 d through an fastening hole 2 h, and folding the tubular portion 3 d over to an outside of the substrate and flattening out the tubular portion 3 d. As shown in FIG. 21, it has been also revealed that the above structure omits the aforementioned need for alterations at the time of assembly to the substrate 2 and also solves the problem where the step adjustment plate 3 is scraped as the defective, since the formed tubular portion 3 d cannot be obliquely bent even when the plurality of step adjustment plates 3 are stacked on top of one another as the inventory products or as the components required in the manufacturing process of the metal gasket.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Publication No. 2002-286141

Patent Literature 2: Japanese Patent Application Publication No. H10-281289

SUMMARY OF INVENTION Technical Problems

Nevertheless, it has been found out that, when a material for deep drawing (e.g. SUS304 or SUS430) is used in the above step adjustment plate 3, due to a low tensile strength and a high elongation of the material, the step adjustment plate 3 is weakened in resistance to expansion and contraction of a cylinder head and a cylinder block during a cold temperature operation of an engine, and can be deformed in an exhaust direction, an intake direction, and other directions, as shown in FIGS. 22A and 22B. The deformation tendency is noticeable especially in an engine with high power and low rigidity, and measures must be taken against the deformation.

One of the measures to cope with the deformation of the step adjustment plate 3 is to increase a thickness of the plate so as to enhance the strength. However, as a result of this method, a strain is increased in the cylinder head and the cylinder block, thereby causing other problems such as increased oil consumption and abnormal noise heard from various components, although this method improves deformation resistance, along with sealing performance against the fuel gas. From the requirement of compatibility between the seal performance of the gasket and the above problems due to the distortion of the cylinder head and the cylinder block, an applicable thickness of a metal foil constituting the step adjustment plate 3 should generally be limited to a range from 0.05 mm to 0.15 mm, and this range restriction in thickness is one of the foremost causes of the deformation. In particular, when an extremely thin metal foil having a thickness of 0.05 mm is utilized to define a slight step, such a deformation must be addressed, which emphasizes the demand for measures to prevent the deformation of the step adjustment plate 3.

Since the aforementioned anti-deformation method of increasing the thickness of the metal foil cannot be adopted to prevent the deformation of the step adjustment plate 3 in view of the above problems, a resilient material such as a stainless steel strip for a spring (e.g. SUS301-1/2H, SUS301-3/4H, and SUS304-3/4H) was used as the metal foil constituting the step adjustment plate 3, and thus formed step adjustment plate 3 was fastened with the substrate 2. However, in this case, the following additional problems emerged.

More particularly, in the circular prepared hole 3 c provided in the protruding piece 3 b of the step adjustment plate 3, the tubular portion 3 d having the circular cross section was formed with use of the die including the cylindrical punch, and the tubular portion 3 d was inserted through the fastening hole 2 h of the substrate 2. Subsequently, the tubular portion 3 d was folded over to an outside of the substrate 2 (i.e. bending process) and flattened out. In this case, as shown in FIG. 23A, cracking can occur anywhere, and if space between cracks is small, engaging force of the folded portion with respect to the substrate 2 is decreased. Furthermore, because of the cracking, the folded portion might fall off the step adjustment plate 3, and the fallen portion can pose a risk of sealing deficiency when entering between the step adjustment plate 3 and the substrate 2, or when left in the die to cause damage to bead portions of the substrate 2. Moreover, as shown in FIG. 23B, even when the prepared hole 3 c having a polygonal shape is provided in the protruding piece 3 b of the step adjustment plate 3 in advance, and the tubular portion 3 d having a polygonal cross section is formed by inserting the die including the cylindrical punch, as shown in FIG. 23C, the use of the resilient material as the step adjustment plate 3 inevitably results in occurrence of the cracks in a middle portion of the tubular portion 3 d or loss of a portion of the tubular portion 3 d.

In light of the above, an objective of the present invention is to provide a method for manufacturing a metal gasket for a cylinder head that is capable of establishing a firmly engaged state between the substrate and the step adjustment plate without suffering the aforementioned occurrence of cracks and deficiency due to loss. Another objective of the present invention is to provide a metal gasket for a cylinder head that is capable of improving the engaging force between the substrate and the step adjustment plate while obtaining an appropriate contact pressure balance by providing the thickness difference between the annular beads and the outer beads by means of a slight step utilizing the metal foil.

Means for Solving the Problem

Thus, the objective of the present invention is to advantageously solve the aforementioned problems, and the present invention provides a method for manufacturing a metal gasket for a cylinder head according to the present invention, the metal gasket including: at least one substrate made of a resilient metal layer and having cylinder holes formed in correspondence with cylinder bores in a cylinder block to be mounted with the cylinder head in an engine, annular beads each formed around a different one of the cylinder holes, coolant holes formed around an outer periphery of each of the annular beads in correspondence with coolant holes of the cylinder head and a cooling water jacket or coolant holes of the cylinder block, and an outer bead formed and positioned to entirely enclose the annular beads and the coolant holes; and a step adjustment plate made of a metal layer and having a plurality of annular portions each disposed over and around an outer periphery of a different one of the cylinder holes of the substrate; and a plurality of protruding pieces formed integrally with each annular portion at a peripheral edge thereof, each protruding piece of the step adjustment plate engaged through the substrate, the method comprising the steps of: forming a prepared hole in each protruding piece of the step adjustment plate; forming a tubular portion including a plurality of projecting segments by inserting a die including a polygonal pyramidal punch into the prepared hole so as to bend up a peripheral portion around the prepared hole while cutting the peripheral portion into segments; forming in the substrate an fastening hole in correspondence with a position of the tubular portion formed in the step adjustment plate; and engaging the protruding piece through the substrate by inserting the tubular portion of the step adjustment plate through the corresponding fastening hole formed in the substrate, and subsequently folding the plurality of projecting segments of the tubular portion over to an outside of the substrate and flattening out the projecting segments. Note that the “polygonal pyramidal shape” herein encompasses the meaning of a truncated polygonal pyramidal shape in which a tip of the punch is flattened or rounded.

According to the above method for manufacturing a metal gasket for a cylinder head, since the die including the polygonal pyramidal punch is used for bending up the peripheral portion around the prepared hole formed in the protruding piece of the step adjustment plate into the tubular shape, a sidewall of the bent-up tubular portion is cut into a plurality of projecting segments having a substantially uniform size by angled edges (joining adjacent conical surfaces and serving as blades) of the punch. Accordingly, by folding the plurality of projecting segments over to the outside and flattening out the projecting segments, a state where the flattened projecting segments are uniformly distributed in a petaloid shape is achieved, whereby the firmly engaged state is established between the substrate and the step adjustment plate. As a result, even when fretting (relative surface motion in a direction parallel to deck surfaces of the cylinder head and the cylinder block) occurs in the deck surfaces in the presence of repeated heating and cooling of the cylinder head and the cylinder block, disengagement of the step adjustment plate from the substrate is prevented. The present invention is particularly advantageous when the resilient material (e.g. stainless steel strip for a spring) is used as a material for the step adjustment plate.

In the above method for manufacturing a metal gasket for a cylinder head, it is preferable that the polygonal pyramidal punch of the die comprises a pentagonal pyramidal punch, and that the plurality of projecting segments of the tubular portion comprises five projecting segments. With the above structure, the plurality of projecting segments of the tubular portion which have been flattened in the petaloid shape are each assured to have a sufficient size to establish the firmly engaged state with respect to the substrate.

Furthermore, in the above method for manufacturing a metal gasket for a cylinder head, it is preferable the punch of the die has a cone angle θ ranging from 20 to 40 degrees. Note that the “cone angle of the punch” herein refers to an angle that the angled edges, which are located in boundaries between adjacent conical surfaces of the polygonal pyramidal punch and serve as blades, form with respect to an axis line of the punch. If the cone angle of the punch is greater than 40 degrees, some parts of the tubular portion cannot be cut into a plurality of segments simultaneously with formation thereof, and discrepancy might occur in number and angle (i.e. an inclination angle of the projecting segments with respect to a plane in which the step adjustment plate extends). On the other hand, if the cone angle of the punch is less than 20 degrees, a press stroke is lengthened, and the tip of the die is thinned, and therefore the die is exposed to increased risk of break-off at the tip during process, although this case presents no problems in terms of forming the tubular portion.

Moreover, in the above method for manufacturing a metal gasket for a cylinder head, it is preferable that a shape of the prepared hole formed in the step adjustment plate is circular. Although it is no problem to form the prepared hole in a polygonal shape in concordance with the shape of the punch, such a polygonal prepared hole in combination with the similarly polygonal punch adversely affects workability in terms of securing positional precision and angular positional precision of the hole and the punch. If the prepared hole is formed in a circular shape, the need for positional alignment and angular positional alignment is omitted, and therefore a favorable quality is maintained while workability is improved.

Moreover, in the above method for manufacturing a metal gasket for a cylinder head, it is preferable that a shape of the fastening hole formed in the substrate is circular. Although it is no problem to form the fastening hole in a polygonal shape in concordance with the cross section of the tubular portion, such a polygonal fastening hole, in combination with the similarly polygonal tubular portion to be inserted into the fastening hole, adversely affects workability in terms of securing the positional precision and the angular positional precision of the fastening hole and the tubular portion. Furthermore, when the fastening hole of the substrate is formed in the polygonal shape, the folding die used for folding the projecting segments of the tubular portion over to the outside and flattening the projecting segments out needs to be formed in the polygonal shape, and workability is adversely affected in terms of securing the positional precision and the angular positional precision of the folding die and the projecting segments. On the other hand, when the fastening hole is formed in the circular shape, the need for the positional alignment and the angular positional alignment is omitted both between the fastening hole and the tubular portion and between the folding die and the projecting segments. Consequently, the favorable quality is maintained while workability is improved.

The present invention also provides a metal gasket for a cylinder head, the metal gasket including: at least one substrate made of a resilient metal layer and having cylinder holes formed in correspondence with cylinder bores in a cylinder block to be mounted with the cylinder head in an engine, annular beads each formed around a different one of the cylinder holes, coolant holes formed around an outer periphery of each of the annular beads in correspondence with coolant holes of the cylinder head and a cooling water jacket or coolant holes of the cylinder block, and an outer bead formed and positioned to entirely enclose the annular beads and the coolant holes; and a step adjustment plate made of a metal layer and having a plurality of annular portions each disposed over and around an outer periphery of a different one of the cylinder holes of the substrate; and a plurality of protruding pieces formed integrally with each annular portion at a peripheral edge thereof, each protruding piece of the step adjustment plate engaged through the substrate, wherein a prepared hole is formed in each protruding piece of the step adjustment plate, and a tubular portion including a plurality of projecting segments is formed by inserting a die including a polygonal pyramidal punch into the prepared hole so as to bend up a peripheral portion around the prepared hole while cutting the peripheral portion into segments, and an fastening hole is formed in the substrate in correspondence with a position of the tubular portion formed in the step adjustment plate, and the protruding piece is engaged through the substrate by inserting the tubular portion of the step adjustment plate through the corresponding fastening hole formed in the substrate, and subsequently folding the plurality of projecting segments of the tubular portion over to an outside of the substrate and flattening out the projecting segments.

In the above metal gasket for a cylinder head according to the present invention, it is preferable that an outer edge surface of each annular portion of the step adjustment plate located closer to the coolant holes is situated outward from an outer edge forming a bead profile of the annular beads. It is also preferable that the outer edge surface is inward from an inner edge of the outer bead formed and positioned to entirely enclose the cooling water jacket or the coolant holes of the cylinder block and the coolant holes.

Effects of the Invention

According to the present invention, a method for manufacturing a metal gasket for a cylinder head that is capable of establishing a firmly engaged state between a substrate and a step adjustment plate, as well as a metal gasket for a cylinder head that is capable of improving an engaging force between the substrate and the step adjustment plate, is provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an entire metal gasket for a cylinder head according to an embodiment in accordance with the present invention.

FIG. 2A is a cross-section view of the metal gasket for a cylinder head according to the above embodiment taken along a line A-A of FIG. 1, and FIG. 2B is a cross-section view taken along a line B-B of FIG. 1.

FIG. 3 is a plan view of a lower substrate of the metal gasket for a cylinder head according to the above embodiment.

FIG. 4 is a plan view of a step adjustment plate of the metal gasket for a cylinder head according to the above embodiment.

FIG. 5 is a plan view of a protruding piece of the step adjustment plate in the metal gasket for a cylinder head according to the above embodiment in a state where a tubular portion is inserted through an fastening hole of the lower substrate and folded over to an outside of the lower substrate.

FIG. 6 is a cross-section view of a metal gasket for a cylinder head according to another embodiment in accordance with the present invention when the metal gasket is viewed from substantially the same position as in FIG. 2A.

FIG. 7 is a plan view of the protruding piece of the step adjustment plate in the metal gasket for a cylinder head according to the other embodiment in a state before the tubular portion is bent up.

FIG. 8A is a side view of the tubular portion formed by directly piercing a pentagonal pyramidal punch without forming the prepared hole, and FIG. 8B is a cross-section view of the tubular portion of FIG. 8A in a state where the tubular portion is inserted through the fastening hole of the substrate and flattened out.

FIG. 9 is a perspective view of a die including the pentagonal pyramidal punch applicable in the present invention.

FIG. 10A is a plan view of the tubular portion formed by the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention, and FIG. 10B is a side view of the same.

FIG. 11 is a side view of the tubular portion formed by the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention in a state where the tubular portion is inserted through the fastening hole of the substrate.

FIG. 12 is a side view of the tubular portion formed by the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention in a state where the tubular portion is folded over to the outside with use of a folding die.

FIG. 13 illustrates the die including polygonal pyramidal punches applicable in the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention, together with a correspondence table regarding cone angles of the punches.

FIG. 14 is a plan view of a state where the die including the pentagonal pyramidal punch is inserted into a pentagonal prepared hole formed in the protruding piece of the step adjustment plate.

FIG. 15 illustrates a tensile test carried out by taking out a portion of the metal gasket manufactured by the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention around where the substrate and the step adjustment plate are engaged with each other.

FIG. 16A is a table showing results of manufacturing verification conducted by varying a blade angle of the punch, and FIG. 16B is a graph showing a relation between the cone angle and cone length.

FIG. 17 is a perspective view of the die including another pentagonal pyramidal punch applicable in the method for manufacturing a metal gasket for a cylinder head in accordance with the present invention.

FIG. 18 is a partially enlarged plan view of a metal gasket according to a conventional technology.

FIG. 19 is a cross-section view of step adjustment plates for metal gaskets according to the conventional technology with the step adjustment plates stacked on top of one another.

FIG. 20 is a cross-section view of a step adjustment plate of a metal gasket according to Comparative Example in a state where the tubular portion having a circular cross section has been formed by applying drawing processing to a peripheral portion around the prepared hole formed in the protruding piece of the step adjustment plate with use of the die including a cylindrical punch.

FIG. 21 is a cross-section view of step adjustment plates for metal gaskets according to Comparative Example with the step adjustment plates stacked on top of one another.

FIG. 22A and FIG. 22B illustrate a state where the step adjustment plate is deformed when a material for deep drawing is used in the step adjustment plate.

FIG. 23A is a plan view of the protruding piece of the step adjustment plate for the metal gasket according to Comparative Example with the tubular portion having the circular cross section folded over to the outside and flattened out, FIG. 23B is a plan view of the protruding piece of the step adjustment plate with the pentagonal prepared hole formed thereon, and FIG. 23C is a plan view showing a state where the tubular portion is folded over to the outside and flattened out, the tubular portion formed by inserting the die including the cylindrical punch into the pentagonal prepared hole formed in the protruding piece of the step adjustment plate.

FIG. 24 is a plan view of the metal gasket for a cylinder head of the above embodiment according to the present invention with the step adjustment plate mounted on the lower substrate.

BEST MODES FOR CARRYING OUT THE INVENTION

The following describes an embodiment according to the present invention in detail with reference to the drawings.

In the present embodiment, a metal gasket 1 for a cylinder head (referred to below simply as the “metal gasket 1”) is a three-layer lamination type that includes three metal layers, inclusive of a step adjustment plate, as well as two substrates 2 as resilient metal layers made of stainless steel, stacked on each other as shown in FIG. 2. As shown in FIGS. 1 and 3, each of the substrates 2 includes: a plurality (three in the drawing) of cylinder holes 2 a formed in correspondence with cylinder bores in a cylinder block to be mounted with a cylinder head in an engine, i.e. an internal combustion engine in which the metal gasket 1 is to be assembled; annular beads 2 b each having an angle cross-section and formed around a different one of the cylinder holes 2 a; a multitude of coolant holes 2 c formed around an outer periphery of each of the annular beads 2 b in correspondence with a cooling water jacket of the cylinder block (in a case of an open deck type cylinder block) or coolant holes of the cylinder block (in a case of a closed deck type cylinder block), as well as coolant holes of the cylinder head; and an outer bead 2 d having a one-sided sloped shape in cross section and formed and positioned to entirely enclose the annular beads 2 b and the coolant holes 2 c.

Outside the outer bead 2 d, each substrate 2 also includes: a plurality of lubricating oil holes 2 e; a plurality (eight in the drawing) of bolt holes 2 f in each of which a head bolt is to be inserted for tightly fastening the cylinder head to the cylinder block; and eyelet holes 2 g. The annular beads 2 b of the two substrates 2 are aligned in a thickness direction of the gasket 1 and externally protruded to face opposite directions. Similarly, the outer beads 2 d of the two substrates 2 are aligned in the thickness direction of the gasket 1 and externally protruded to face opposite directions.

Furthermore, as shown in FIG.3, in this example, the lower substrate 2 facing the deck surface of the cylinder block includes four or five fastening holes 2 h circumferentially formed near the outer periphery of each annular bead 2 b around a corresponding cylinder hole 2 a at an appropriate interval in correspondence with positions of the cooling water jacket of the cylinder block (in the case of an open deck type cylinder block) or the coolant holes of the cylinder block (in the case of the closed deck type cylinder block), as well as the coolant holes of the cylinder head.

Moreover, as shown in FIG. 4, the metal gasket 1 of the present embodiment includes a step adjustment plate 3 interposed between the two substrates 2. The step adjustment plate 3 is a metal layer that is thinner than the substrates 2 (e.g. from 0.01 mm to 0.15 mm in thickness) and is made of stainless steel (preferably, a resilient material such as a stainless steel strip for a spring). The step adjustment plate 3 includes: three annular portions 3 a each disposed, with respect to each substrate 2, over and around the periphery of a different one of the cylinder holes 2 a; and protruding pieces 3 b formed integrally with each of the annular portions 3 a at a peripheral edge thereof. The three annular portions 3 a are connected with one another. The protruding pieces 3 b protrude outward from the peripheral edge of each annular portion 3 a and extend at least to a position of the cooling water jacket or positions of the coolant holes of the cylinder block. In this example, four or five protruding pieces 3 b are provided in each annular portion 3 a in correspondence with the four or five fastening holes 2 h formed around each cylinder hole 2 a in the lower substrate 2. As shown in FIG. 5, each protruding piece 3 b is firmly hooked through the lower substrate 2 at five projecting segments 3 d ₁ (crimped segments) flattened in a petaloid shape. The projecting segments 3 d ₁ are described later.

Note that, as FIG. 2B shows a relation between the step adjustment plate 3 and the annular beads 2 b in a widthwise direction thereof, an outer edge surface of each annular portion 3 a of the step adjustment plate 3 located closer to the coolant holes is situated outward from an outer edge L2 forming a bead profile of the annular beads 2 b in FIG. 2B. In other words, the step adjustment plate 3 is disposed to cover the entire annular bead in the widthwise direction.

FIG. 6 is a cross-section view of the metal gasket 1 of another embodiment according to the present invention when the metal gasket 1 is viewed from substantially the same position as in FIG. 2A. The other embodiment differs from the above embodiment only in that the projecting direction of the annular beads 2 b and the outer bead 2 d is modified so that the beads 2 b and 2 d face each other, and apart from this point, the other embodiment has substantially the same structure as the above embodiment.

According to the metal gasket 1 of the above two embodiments, owing to the plurality of projecting segments 3 d ₁ folded over across a corresponding fastening hole 2 h and flattened out, the firmly engaged state is established between the substrate 2 and the step adjustment plate 3. As a result, even when the fretting (relative surface motion in the direction parallel to the deck surfaces) occurs in the deck surfaces in the presence of repeated heating and cooling of the cylinder head and the cylinder block, the disengagement of the step adjustment plate from the substrate is prevented.

Furthermore, according to the metal gasket 1 of the above two embodiments, as shown in FIG. 2A, since an entire bead area ranging from an inner edge L1 to the outer edge L2 of the annular bead 2 b rests on the step adjustment plate 3, step differences are provided between the annular beads 2 b and the outer beads 2 d in the substrates 2. As a result, surface pressure to the annular beads 2 b and the outer beads 2 d is improved, and therefore, the entire annular beads 2 d are allowed to be compressed. In particular, even when the extremely thin metal foil having the thickness of 0.05 mm is used, the surface pressure balance is appropriately adjusted by the slight step.

Moreover, according to the metal gasket 1 of the above two embodiments, since the fastening holes 2 h for insertion of the tubular portions 3 d are formed along the peripheries of the annular beads in correspondence with the coolant holes of the cylinder head, and the cooling water jacket or the coolant holes of the cylinder block, a portion of each tubular portion that are folded over to the outside and flattened out can enter a corresponding coolant or a corresponding cooling water jacket without sandwiched between the deck surface of the cylinder head and that of the cylinder block.

Consequently, the folded and flattened portion is prevented from becoming an obstacle to an increase in the surface pressure in the annular beads 2 b.

Moreover, according to the metal gasket 1 of the above two embodiments, since the number of the projecting segments 3 d ₁ formed in each protruding piece 3 b is five, when flattened into the petaloid shape with a plurality of petals, the projecting segments 3 d ₁ of the tubular portion 3 d surely have a sufficient size to establish the firmly engaged state with respect to the substrate 2.

Moreover, according to the metal gasket 1 of the above two embodiments, the number of the fastening holes 2 h formed in the substrate 2 for engagement of the protruding pieces 3 b is set to be four or five in correspondence with each cylinder bore, the engaging force of the step adjustment plate 3 to the substrate 2 is sufficiently enhanced so that the disengagement of the step adjustment plate 3 from the substrate 2 is prevented even when the fretting occurs in the deck surfaces of the cylinder head and the cylinder block.

Next, a description is given of a method for manufacturing the metal gasket 1 according to the above embodiments.

To begin with, as shown in an enlarged manner in FIG. 7, the prepared hole 3 c is formed at an upper end portion of each protruding piece 3 b of the step adjustment plate 3. The reason why the prepared hole 3 c is formed in the protruding piece 3 b is that, if the pentagonal pyramidal punch is directly pierced into the protruding piece 3 b in order to form the tubular shape, and the formed tubular portion 3 d is inserted through the fastening hole 2 h of the substrate 2 for folding and flattening process, a tip of the tubular portion 3 d might be bent over, which poses a risk that the step adjustment plate 3 might not be completely integrated with the substrate 2. This is because the tip of the tubular portion 3 d is turned outward once the tubular portion 3 b is bent up (refer to FIG. 8A), and during the immediately subsequent flattening process, the outwardly-turned portion is bent over inward (refer to FIG. 8B).

Subsequently, the drawing processing is applied to the peripheral portion around the prepared hole 3 c formed in each protruding piece 3 b by inserting a die 4 including a polygonal pyramidal (pentagonal pyramidal in this example) punch 4 a. By doing so, as shown in FIGS. 10A and 10B, the peripheral portion is bent up into the tubular shape while cut into the plurality of segments by the blades (angled edges) 4 b of the punch 4 a, thus forming the tubular portion 3 d composed of the plurality of projecting segments 3 d ₁. As for a height of the tubular portion 3 d, as shown in FIG. 10B, the height of 1 mm is sufficient enough, for example. Meanwhile, a portion of the die 4 below the punch 4 a is made cylindrical.

Subsequently, the step adjustment plate 3 in which the tubular portion 3 d has been bent up in each protruding piece 3 b as described above is disposed on the lower substrate 2 shown in FIG. 3. At this time, the three annular portions of the step adjustment plate 3 and the peripheries of the three cylinder holes 2 a are aligned one above another, and as shown in FIG. 11, the tubular portion 3 d of each protruding piece 3 b is inserted through a corresponding fastening hole 2 h formed in the substrate 2. Note that the circular fastening holes 2 h that preferably have a circular shape can be formed in the bottom substrate 2 at any timing in advance.

Subsequently, as shown in FIG. 12, the projecting segments 3 d ₁ of the tubular portion 3 d of each protruding piece 3 b inserted through the corresponding fastening hole 2 h are folded over to the outside with use of a die 5 including a punch having a conically-shaped tip, for example. In this circumstance, since the tubular portion 3 d has been cut into the plurality (five in this case) of projecting segments 3 d ₁ having a substantially uniform size, the tubular portion 3 d is uniformly bent into the petaloid shape with the plurality of petals when folded over to the outside.

Then, the petaloid-shaped projecting segments 3 d ₁ of the tubular portion 3 d are flattened out with use of the die (not shown) including a punch having a flat tip, for example. As a result, as shown in FIG. 5, the tubular portion 3 d is flattened in the petaloid shape with the plurality of petals of the substantially uniform size, with each projecting segment 3 d ₁ having the sufficient size to be hooked against the substrate 2.

In this way, the step adjustment plate 3 engages with the lower substrate 2 via the tubular portions 3 d of the protruding pieces 3 b, and then, as shown in FIG. 2A, an upper substrate 2 is placed over the step adjustment plate 3 and processed as shown in FIG. 24. Subsequently, the three cylinder holes 2 a of each of the lower and the upper substrate 2 are aligned one above another. Furthermore, although not shown, typical grommets are inserted into the eyelet holes 2 g of each of the lower and the upper substrate 2 aligned one above another and compressed, so that the two substrates 2 and the step adjustment plate 3 interposed therebetween are maintained in a fixed position. It should be noted that the eyelet holes 2 g are provided outward from an area of the cylinder block and the cylinder head of the engine, and therefore the grommets are prevented from decreasing the surface pressure of the beads 2 b and 2 d by sandwiched between the deck surfaces of the cylinder block and the cylinder head of the engine.

According to the method for manufacturing the metal gasket 1, since the die 4 including the polygonal pyramidal punch 4 a is used for bending up the peripheral portion around each prepared hole 3 c formed in the protruding piece 3 b of the step adjustment plate 3 into the tubular shape, the sidewall of the bent-up tubular portion 3 d is cut into the plurality of projecting segments 3 d ₁ having the substantially uniform size by the blades 4 d (i.e. angled edges joining adjacent conical surfaces) of the punch 4 a. By folding the above plurality of projecting segments 3 d ₁ to the outside and flattening out the projecting segments 3 d ₁, the state where the projecting segments 3 d ₁ are flattened in the petaloid shape in a uniformly distributed manner is achieved, whereby the firmly engaged state is established between the substrate 2 and the step adjustment plate 3. As a result, even when the fretting (relative surface motion in the direction parallel to the deck surfaces) occurs in the deck surfaces in the presence of repeated heating and cooling of the cylinder head and the cylinder block, the disengagement of the step adjustment plate 3 from the substrate 2 is prevented. The present manufacturing method is particularly advantageous when the resilient material (e.g. stainless steel strip for a spring) is used as the material for the step adjustment plate 3.

In the method for manufacturing the metal gasket 1, it is preferable that the polygonal pyramidal punch 4 a of the die 4 comprises a pentagonal pyramidal punch, and the plurality of projecting segments 3 d ₁ of the tubular portion 3 d comprises five projecting segments. With the above structure, the projecting segments 3 d ₁ of the tubular portion 3 d which have been flattened into the petal shape are each assured to have a sufficient size to establish the firmly engaged state with respect to the substrate 2.

Furthermore, in the above method for manufacturing a metal gasket 1, it is preferable that the punch 4 a of the die 4 has a cone angle θ ranging from 20 to 40 degrees. Note that the “cone angle θ of the punch” herein refers to an angle that the angled edges, which are located in boundaries between adjacent conical surfaces of the polygonal pyramidal punch and serve as blades, form with respect to an axis line S of the punch. If the cone angle θ of the punch is greater than 40 degrees, some parts of the tubular portion 3 d cannot be cut into a plurality of segments simultaneously with formation thereof, and discrepancy might occur in number and angle (i.e. an inclination angle of the projecting segments 3 d ₁ with respect to a plane in which the step adjustment plate 3 extends). On the other hand, if the cone angle θ of the punch is less than 20 degrees, a press stroke is lengthened, and the tip of the die is thinned, and therefore the die is exposed to increased risk of break-off at the tip during the process, although this case presents no problems in terms of forming the tubular portion 3 d.

Moreover, in the above method for manufacturing the metal gasket, it is preferable that a shape of the prepared hole 3 c formed in the step adjustment plate 3 is circular. Although it is no problem to form the prepared hole 3 c in a polygonal shape in concordance with the shape of the punch, as shown in FIG. 14, such a polygonal prepared hole in combination with the similarly polygonal pyramidal punch adversely affects workability in terms of securing positional precision and angular positional precision of the hole 3 c and the punch. On the other hand, when the prepared hole 3 c is formed in a circular shape, the need for positional alignment and angular positional alignment is omitted, and therefore, a favorable quality is maintained while workability is improved.

Moreover, in the above method for manufacturing the metal gasket, it is preferable that a shape of the fastening hole 2 h formed in the substrate 2 is circular.

Although it is no problem to form the fastening hole 2 h in a polygonal shape in concordance with the cross section shape of the tubular portion 3 d, such a polygonal fastening hole 2 h, in combination with the similarly polygonal tubular portion 3 d to be inserted into the fastening hole 2 h, adversely affects workability in terms of securing the positional precision and the angular positional precision of the fastening hole 2 h and the tubular portion 3 d. Furthermore, when the fastening hole 2 h in the substrate 2 is formed in the polygonal shape, the folding die used for folding the projecting segments 3 d ₁ of the tubular portion 3 d over to the outside and flattening out the projecting segments 3 d ₁ needs to be in the polygonal shape, and workability is adversely affected in terms of securing the positional precision and the angular positional precision of the folding die and the projecting segments 3 d ₁. On the other hand, when the fastening hole 2 h is formed in the circular shape, the need for the positional alignment and the angular positional alignment is omitted both between the fastening hole 2 h and the tubular portion 3 d and between the folding die and the projecting segments 3 d ₁. Consequently, the favorable quality is maintained while workability is improved.

EXAMPLES

As shown in FIG. 15, in order to confirm the effects achieved by the method for manufacturing a metal gasket for a cylinder head according to the present invention, portions (test pieces) in which the substrate 2 and the step adjustment plate 3 are coupled were collected through the method for manufacturing a metal gasket for a cylinder head according to a first example of the present invention (referred to below as the “manufacturing method of Example 1”, the method for manufacturing a metal gasket for a cylinder head according to a second example of the present invention (referred to below as the “manufacturing method of Example 2”, and the method for manufacturing a metal gasket for a cylinder head according to a third example of the present invention (referred to below as the “manufacturing method of Example 3”, and coupling strength between the substrate 2 and the step adjustment plate 3 was evaluated for each test piece by means of a tensile test apparatus.

The manufacturing method of Example 1 comprises, for engaging the step adjustment plate 3 with the substrate 2, the steps of: forming the pentagonal prepared hole 3 c in each protruding piece 3 b of the step adjustment plate 3; forming the tubular portion 3 d including five projecting segments 3 d ₁ by inserting the die 4 including the pentagonal pyramidal punch 4 a into the prepared hole 3 c; forming in the substrate 2 a pentagonal fastening hole 2 h in correspondence with the position of the tubular portion 3 d formed in the step adjustment plate 3; and inserting the tubular portion 3 d of the step adjustment plate 3 through the corresponding fastening hole 2 h formed in the substrate 2, and subsequently folding the projecting segments 3 d ₁ of the tubular portion 3 d to the outside and flattening out the projecting segments 3 d ₁ with use of the pentagonal folding die.

The manufacturing method of Example 2 comprises, for engaging the step adjustment plate 3 with the substrate 2, the steps of: forming the circular prepared hole 3 c in each protruding piece 3 b of the step adjustment plate 3; forming the tubular portion 3 d including five projecting segments 3 d ₁ by inserting the die 4 including the pentagonal pyramidal punch 4 a into the prepared hole 3 c; forming in the substrate 2 a pentagonal fastening hole 2 h in correspondence with the position of the tubular portion 3 d formed in the step adjustment plate 3; and inserting the tubular portion 3 d of the step adjustment plate 3 through the corresponding fastening hole 2 h formed in the substrate 2, and subsequently folding the projecting segments 3 d ₁ of the tubular portion 3 d to the outside and flattening out the projecting segments 3 d ₁ with use of the pentagonal folding die.

The manufacturing method of Example 3 comprises, for engaging the step adjustment plate 3 with the substrate 2, the steps of: forming the circular prepared hole 3 c in each protruding piece 3 b of the step adjustment plate 3; forming the tubular portion 3 d including five projecting segments 3 d ₁ by inserting the die 4 including the pentagonal pyramidal punch 4 a into the prepared hole 3 c; forming in the substrate 2 a circular fastening hole 2 h in correspondence with the position of the tubular portion 3 d formed in the step adjustment plate 3; and inserting the tubular portion 3 d of the step adjustment plate 3 through the corresponding fastening hole 2 h formed in the substrate 2, and subsequently folding the projecting segments 3 d ₁ of the tubular portion 3 d to the outside and flattening out the projecting segments 3 d ₁ with use of the pentagonal folding die.

The portions around where the substrate and the step adjustment plate are engaged with each other were collected with respect to the respective gaskets manufactured according to the aforementioned three types of manufacturing methods, and the tensile tests were carried out as shown in FIG. 15. As a result, in none of the three manufacturing methods according to the present invention, the gasket was not broken until test force reaches 200N and it exhibited a sufficient coupling strength. The differences in the manufacturing method did not yield any difference in terms of coupling strength. Furthermore, when the tubular portion 3 d was formed in the protruding piece 3 b of the step adjustment plate 3 with use of the punch 4 a, the undesired crack or the loss of the projecting segments 3 d ₁ was not seen in the tubular portion 3 d at all, except for those in the cut portions between adjacent projecting segments 3 d ₁.

Accordingly, from the above test results, it was found out that the metal gasket 1 capable of improving the engaging force between the substrate 2 and the step adjustment plate 3 was manufacturable at low cost and in a stable manner as long as the manufacturing method of Example 3 is used, i.e. the tubular portion 3 d is formed from the peripheral portion around the prepared hole 3 c with use of the die 4 including the pentagonal pyramidal punch 4 a, and that there is no need to adopt the manufacturing methods of Examples 1 and 2 which are inferior in terms of workability because of the importance of the positional precision and the angular positional precision of the hole.

Next, a description is given of work tests on the tubular portion 3 d carried out by varying the cone angle θ (blade angle) of the pentagonal pyramidal punch. In the work tests, five dies 4 in which the cone angles θ of the punches 4 a of 10 degrees, 20 degrees, 30 degrees, 40 degrees, and 60 degrees were used. FIG. 16A shows results of the tests. As can be seen from the test results, in the case of the die 4 in which the cone angles θ of the punch 4 a is 60 degrees, the discrepancy sometimes occurred in number and angle of the cut projecting segments 3 d ₁, and the processing turned out to be unstable. On the other hand, as shown in FIG. 16B, in the case of the die 4 in which the cone angles θ of the punch 4 a is 10 degrees, the press stroke is lengthened, and the tip of the die is thinned, and therefore the die is exposed to the increased risk of break-off at the tip during the process, although this case presents no problems in terms of forming the tubular portion 3 d. From the above, it is understood that the cone angle θ of the punch 4 a is preferably in the range from approximately 20 to 40 degrees.

Although the present invention has been described based on the example shown in the drawings, the present invention is not limited to the example described above. For example, the shape of the prepared hole 3 c formed in each protruding piece 3 b may be any other polygon such as square and hexagon. Furthermore, the fastening holes 2 h may be formed in the upper substrate 2 for engagement of the tubular portions 3 d of the step adjustment plate 3. Moreover, as shown in FIG. 17, the die 4 to be inserted into the prepared hole 3 c formed in the protruding piece 3 b for formation of the tubular portion 3 d having the polygonal cross-section may include the punch 4 a having the truncated polygonal pyramidal shape in which the tip of the punch 4 a is flattened or rounded.

INDUSTRIAL APPLICABILITY

Thus, according to the present invention, the method for manufacturing a metal gasket for a cylinder head that is capable of establishing the firm engaged state between the substrate and the step adjustment plate, as well as the metal gasket for a cylinder head that is capable of improving the engaging force between the substrate and the step adjustment plate made of the resilient metal foil having the thickness ranging from 0.05 mm to 0.15 mm, is provided.

REFERENCE SIGNS LIST

-   1 metal gasket for cylinder head -   2 substrate -   3 step adjustment plate -   3 a annular portion -   3 b protruding piece -   3 c prepared hole -   3 d tubular portion -   3 d ₁ projecting segments -   4 die -   4 a punch 

1. A method for manufacturing a metal gasket for a cylinder head, the metal gasket including: at least one substrate made of a resilient metal layer and having cylinder holes formed in correspondence with cylinder bores in a cylinder block to be mounted with the cylinder head in an engine, annular beads each formed around a different one of the cylinder holes, coolant holes formed around an outer periphery of each of the annular beads in correspondence with coolant holes of the cylinder head and a cooling water jacket or coolant holes of the cylinder block, and an outer bead formed and positioned to entirely enclose the annular beads and the coolant holes; and a step adjustment plate made of a metal layer and having a plurality of annular portions each disposed over and around an outer periphery of a different one of the cylinder holes of the substrate; and a plurality of protruding pieces formed integrally with each annular portion at a peripheral edge thereof, each protruding piece of the step adjustment plate engaged through the substrate, the method comprising the steps of: forming a prepared hole in each protruding piece of the step adjustment plate forming a tubular portion including a plurality of projecting segments by inserting a die including a polygonal pyramidal punch into the prepared hole so as to bend up a peripheral portion around the prepared hole while cutting the peripheral portion into segments; forming in the substrate a fastening hole in correspondence with a position of the tubular portion formed in the step adjustment plate; and engaging the protruding piece through the substrate by inserting the tubular portion of the step adjustment plate through the corresponding fastening hole formed in the substrate, and subsequently folding the plurality of projecting segments of the tubular portion over to an outside of the substrate and flattening out the projecting segments.
 2. The method according to claim 1, wherein the polygonal pyramidal punch of the die comprises a pentagonal pyramidal punch, and the plurality of projecting segments of the tubular portion comprises five projecting segments.
 3. The method according to claim 1, wherein the punch of the die has a cone angle (θ) ranging from 20 to 40 degrees.
 4. The method according to claim 1, wherein a shape of the prepared hole formed in the step adjustment plate is circular.
 5. The method according to claim 1, wherein a shape of the fastening hole formed in the substrate is circular.
 6. A metal gasket for a cylinder head, the metal gasket including: at least one substrate made of a resilient metal layer and having cylinder holes formed in correspondence with cylinder bores in a cylinder block to be mounted with the cylinder head in an engine, annular beads each formed around a different one of the cylinder holes, coolant holes formed around an outer periphery of each of the annular beads in correspondence with coolant holes of the cylinder head and a cooling water jacket or coolant holes of the cylinder block, and an outer bead formed and positioned to entirely enclose the annular beads and the coolant holes; and a step adjustment plate made of a metal layer and having a plurality of annular portions each disposed over and around an outer periphery of a different one of the cylinder holes of the substrate; and a plurality of protruding pieces formed integrally with each annular portion at a peripheral edge thereof, each protruding piece of the step adjustment plate engaged through the substrate, wherein a prepared hole is formed in each protruding piece of the step adjustment plate, and a tubular portion including a plurality of projecting segments is formed by inserting a die including a polygonal pyramidal punch into the prepared hole so as to bend up a peripheral portion around the prepared hole while cutting the peripheral portion into segments, and an fastening hole is formed in the substrate in correspondence with a position of the tubular portion formed in the step adjustment plate, and the protruding piece is engaged through the substrate by inserting the tubular portion of the step adjustment plate through the corresponding fastening hole formed in the substrate, and subsequently folding the plurality of segments of the tubular portion over to an outside of the substrate and flattening out the projecting segments.
 7. The metal gasket according to claim 6, wherein an outer edge surface of each annular portion of the step adjustment plate located closer to the coolant holes is situated outward from an outer edge. forming a bead profile of the annular beads and inward from an inner edge of the outer bead formed and positioned to entirely enclose the cooling water jacket or the coolant holes of the cylinder block and the coolant holes.
 8. The method according to claim 1, wherein the substrate is a first substrate, the method further comprising: disposing the step-adjustment plate between the first substrate and a second substrate, the second substrate defining cylinder holes, annular beads, coolant holes, and an outer bead that register with the cylinder holes, annular beads, coolant holes, and outer bead, respectively, of the first substrate; and coupling the second substrate to the step-adjustment plate in the same manner as the first substrate is coupled to the step-adjustment plate.
 9. The metal gasket according to claim 6, wherein the substrate and step-adjustment plate are both made of a resilient metal.
 10. The metal gasket according to claim 6, wherein the tubular portions are formed by inserting a die including a polygonal pyramidal punch into the respective prepared hole to bend upward a peripheral portion of the prepared hole while cutting the peripheral portion into segments.
 11. The metal gasket according to claim 6, wherein the substrate is a first substrate, the gasket further comprising a second substrate, wherein the step-adjustment plate is disposed between the first and second substrates. 